1. Field of the Invention
The present invention relates to a press, having at least one pressing column and a ram pivotally mounted to said at least one pressing column, which ram is adapted to be connected to at least one tool for a shape producing working of a strip-shaped workpiece which is advanced step by step, which press includes a machine frame and a drive shaft which is supported in the machine frame and includes at least one connecting rod unit which is supported eccentrically on said drive shaft.
2. Description of the Prior Art
In the corresponding technical field such presses are defined as punch presses and the present invention relates specifically to a so-called high-speed punch press. In these days such presses are designed to have a large rated force and having large spaces for a mounting of tools. The rams are driven from a drive shaft of the punch press via an arrangement of force-transmitting elements which in turn must be of a very rigid design, which must have a high spring rate and accordingly feature large masses.
Conclusively, extremely high masses are moved at extremely high numbers of stroke in such high-speed punch presses, wherewith very high mass forces as well as high acceleration and deceleration forces occur.
In operation of a high speed punch press not only extremely large forces of inertia and moments of inertia are generated by the ram and the force transmitting elements, but also extremely large forces and moments due to imbalances which must be balanced. In order to balance the forces and moments of the imbalance, balancing weight devices, that is balancing masses are needed, which generate in turn additional forces and moments of inertia and produce in their bearings and in the bearings of their drive members frictional forces.
Furthermore, such punch presses are subject to high demands regarding the precision and quality of the products produced thereon.
A great many punch presses have become known which feature excellent structural solutions to the individual problems described above, however, designs which are advantageous for a given problem area lead often to drawbacks in a further, different problem area.
The punch press according to CH-A-543 376 displays for instance a large distance between the pressure columns which has an advantageous effect on the ram regarding its rigidity against tilting. Furthermore, the structural members which transmit the drive force from the drive shaft onto the ram are designed in such a manner, that the masses which oscillate in the vertical direction are balanced to the largest extent. However, there are still balancing weight units necessary for a complete balancing of the masses oscillating in the vertical direction, with the effect that additional forces of inertia and frictions in bearings are produced. Specifically, the design of the members of the machine which transmit the drive force from the drive shaft onto the ram is such that long paths of the transmittal of forces are present, wherewith a larger spring elasticity of the machine is produced which has a detrimental effect onto the punching process. The structural members which are used for adjusting the height position of the ram and are located at the point of reversing of the forces, i.e. the bearing point of the double arm lever of mentioned punch press, are loaded with twice the punching force.
The CA-A 574 323 discloses a punch press in which the parts of the machine which transmit the driving force from the drive shaft onto the ram form no long paths of transmittal of the forces. Due to the distribution of the forces via the single arm levers, the forces acting onto the connecting rod and onto the structural members for the adjusting of the height position of the ram are reduced. The pressure columns feature, however, a small distance from each other, which is a drawback regarding the rigidity of the ram against tilting. Furthermore, large balancing masses are needed which generate correspondingly high forces of inertia, high moments of inertia, and bearing frictions.